This invention relates to electronic article surveillance (EAS) systems and, in particular, to methods and apparatus for improving these systems.
In a typical EAS system, a protection zone is established through which articles must pass and which is under surveillance by the system. If an article having an EAS tag passes through the protection zone, the system detects the tag and, therefore, the article. The system then activates an alarm, thereby indicating the presence of a tagged article in the protection zone.
As can be appreciated, the reliability of an EAS system depends upon the system alarming only when tags within the protection zone cause the system to alarm. In order to promote reliability, most systems are configured so that a transition zone is provided between the protection zone and the other areas of the site or premises, i.e., the unprotected areas containing tagged articles for display and sale. The transition zone is devoid of such articles. Accordingly, the transition zone allows for a certain degree of expansion of the transmitted EAS signal beyond the protection zone, without the worry of false alarming the EAS system, i.e., alarming the system with tagged articles being displayed for sale.
While the use of a transition zone is beneficial for preventing false alarms, there is also a desire to minimize this zone so as not to waste valuable selling floor space. Realizing a transition zone of minimum extent concurrently with minimizing false alarming has not been easy to achieve.
One reason for this is that the transmitted signal is usually in the form of a transmitted field, i.e., a magnetic, electric or electromagnetic field or a combination thereof. Such, fields change in size and, therefore, may expand or contract with time.
These changes may occur due to environmental conditions such as temperature and power line levels. They may also occur due to field reflecting or absorbing objects (e.g., metal racks and doors as well as non-metal objects such as human beings) which interact with the transmitted field.
Another reason is that the distance of the tagged articles to the transition and protection zones may change. This occurs because the tagged articles may be moved by personnel not aware of these zones. However, moving the tagged articles for display into the transition zone can result in false alarms.
In present day EAS systems, the transition zone is usually determined on-site. Articles with tags are first brought into the protection zone until the EAS system alarms. The tagged articles are then moved slightly out of the zone, until the alarming stops. This establishes the desired transition zone.
Unfortunately, this procedure does not always account for the above-described expansion which might occur in the transmitted field. As a result, false alarms may likely result. These are usually corrected for by dispatching EAS personnel to the site. At the site, the transition zone is again reestablished by the EAS personnel by slightly moving the tagged articles further away from the protection zone until any false alarming stops. While this procedure offers a way of establishing and maintaining a transition zone, it is manpower intensive and, therefore, costly.
It is, therefore, an object of the present invention to provide an EAS system and method which do not suffer from the above disadvantages.
It is a further object of the present invention to provide an EAS system and method in which a transition zone can be established in a manner which preserves selling floor space as well as minimizes false alarms.
It is yet a further object of the present invention to provide an EAS system and method in which a transition zone can be easily and readily established and maintained.